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Stanford scientists track tiny atmospheric ripples using data from internet-beaming balloons:
Giant balloons launched into the stratosphere to beam internet service to Earth have helped scientists measure tiny ripples in our upper atmosphere, uncovering patterns that could improve weather forecasts and climate models.
The ripples, known as gravity waves or buoyancy waves, emerge when blobs of air are forced upward and then pulled down by gravity. Imagine a parcel of air that rushes over mountains, plunges toward cool valleys, shuttles across land and sea and ricochets off growing storms, bobbing up and down between layers of stable atmosphere in a great tug of war between buoyancy and gravity. A single wave can travel for thousands of miles, carrying momentum and heat along the way.
[...] Published Aug. 30 in the Journal of Geophysical Research: Atmospheres, the new research draws on superpressure balloon data from the company Loon LLC, which designed the balloons to provide internet access to areas underserved by cell towers or fiber-optic cables. Spun out of Google parent company Alphabet in 2018, Loon has sent thousands of sensor-laden balloons sailing 12 miles up in the stratosphere – well above the altitude of commercial planes and most clouds – for 100 days or more at a stretch.
[...] The Loon data proved particularly valuable for calculating high-frequency gravity waves, which can rise and fall hundreds of times in a day, over distances ranging from a few hundred feet to hundreds of miles. “They’re tiny and they change on timescales of minutes. But in an integrated sense, they affect, for instance, the momentum budget of the jet stream, which is this massive planetary scale thing that interacts with storms and plays an important role in setting their course,” Sheshadri said.
Journal Reference:
Erik A. Lindgren, Aditi Sheshadri, Aurélien Podglajen, et al. Seasonal and Latitudinal Variability of the Gravity Wave Spectrum in the Lower Stratosphere, Journal of Geophysical Research: Atmospheres (DOI: 10.1029/2020JD032850)
(Score: 0) by Anonymous Coward on Sunday September 06 2020, @08:04AM
Gravity waves are not the same as gravitational waves. There is already a correct explanation in this thread from stormwyrm but I'll offer one as well.
Let's take a parcel of air. Imagine a balloon with 1 kg of air inside of it. In parcel theory, the air inside the parcel doesn't mix with its surroundings. This assumption is imperfect but it's a decent approximation of the atmosphere. Let's forget about moisture. We'll assume that the temperature in the atmosphere cools at a rate of 6 K/km, which is a reasonable estimation of the real atmosphere. Our parcel obeys the first law of thermodynamics so the air inside cools or warms at a rate of 9.8 K/km when the parcel ascends or descends, respectively. We'll ignore the effect of friction for this example, though it is a factor in the real atmosphere.
Initially, our parcel is the same temperature as its surroundings. Let's say it's mechanically lifted up 1 km. The air inside is 6 K colder at this level, but the parcel is 9.8 K colder than originally, or 3.8 K colder than its surroundings. The negatively buoyant parcel experiences a downward acceleration, acquiring momentum as it descends. When the parcel reaches its original level, it's back to the same temperature as its surroundings, but it has downward momentum so it overshoots its original level. Because our model is frictionless, the parcel becomes warmer than its surroundings and becomes positively buoyant, generating an upward acceleration. Eventually the parcel reaches a level 1 km below its original level, where it is 9.8 K warmer, but the surroundings are only 6 K warmer than at the original level. The parcel is 3.8 K warmer than its surroundings. It experiences upward acceleration, ascending to its original level, which it then overshoots due to the momentum it acquired. And the process repeats with the parcel oscillating about its original level.
These waves are oscillations in the atmosphere where gravity is the restoring force. My simplifying assumptions of no friction or mixing prevented damping of the gravity waves, but even with those processes, gravity waves still have a significant effect on weather and climate.